Welcome to the board. Probably not your issue, but I had to tell a story. I had folks handcranking one of my 99s at a fair and one of the threads kept braking. I thought I hadn't changed anything. But I do live in Kansas. The wind was blowing the thread off the take up lever into places it shouldn't. I turned the machine 90 degrees and it was fine the rest of the day. Do you have a fan on?.